Kitagawa Munenori, Xu Xiaosa, Jackson David
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA.
Commun Integr Biol. 2022 Jul 6;15(1):158-163. doi: 10.1080/19420889.2022.2095125. eCollection 2022.
Multicellular organisms use transcripts and proteins as signaling molecules for cell-to-cell communication. Maize KNOTTED1 (KN1) was the first homeodomain transcription factor identified in plants, and functions in maintaining shoot stem cells. KN1 acts non-cell autonomously, and both its messenger RNA (mRNA) and protein traffic between cells through intercellular nanochannels called plasmodesmata. KN1 protein and mRNA trafficking are regulated by a chaperonin subunit and a catalytic subunit of the RNA exosome, respectively. These studies suggest that the function of KN1 in stem cell regulation requires the cell-to-cell transport of both its protein and mRNA. However, hybridization experiments published 25 years ago suggested that mRNA was missing from the epidermal (L1) layer of shoot meristems, suggesting that only the KN1 protein could traffic. Here, we show evidence that mRNA is present at a low level in L1 cells of maize meristems, supporting an idea that both KN1 protein and mRNA traffic to the L1 layer. We also summarize mRNA expression patterns of KN1 homologs in diverse angiosperm species, and discuss KN1 trafficking mechanisms.
多细胞生物利用转录本和蛋白质作为细胞间通讯的信号分子。玉米的结瘤1（KN1）是植物中鉴定出的首个同源异型结构域转录因子，其功能是维持茎干细胞。KN1的作用是非细胞自主性的，其信使核糖核酸（mRNA）和蛋白质都通过称为胞间连丝的细胞间纳米通道在细胞间运输。KN1蛋白和mRNA的运输分别受伴侣蛋白亚基和RNA外切体的催化亚基调控。这些研究表明，KN1在干细胞调控中的功能需要其蛋白质和mRNA在细胞间运输。然而，25年前发表的杂交实验表明，茎尖分生组织的表皮（L1）层中缺少mRNA，这表明只有KN1蛋白能够运输。在这里，我们展示了证据，证明玉米分生组织的L1细胞中存在低水平的mRNA，支持了KN1蛋白和mRNA都运输到L1层的观点。我们还总结了不同被子植物物种中KN1同源物的mRNA表达模式，并讨论了KN1的运输机制。
